Altered control of the differentiated state of the smooth muscle cell (SMC) or SMC phenotypic switching, is implicated in the pathogenesis of a number of major human diseases including atherosclerosis, hypertension, cancer, and asthma which collectively account for >50% of deaths and health care costs in developed societies. However, our understanding the precise role of SMC phenotypic switching in these diseases, and the mechanisms that control SMC phenotypic switching in vivo have been greatly confounded because this process is characterized by loss of expression of SMC marker genes required to identify the cells, and many SMC genes can be expressed by other cell types. Of major significance, studies employing unique SMC- pericyte (SMC-P) lineage tracing mice developed by the Owens lab provide evidence that: 1) the majority of phenotypically modulated SMC-P within atherosclerotic lesions or models of injury-repair in vivo show no detectible expression of SMC markers and can only be identified using rigorous lineage tracing methods; and 2) SMC-P de-differentiate and give rise to multiple other cell types following naphthalene-induced lung injury wherein they appear to trans-differentiate into non-ciliated lung epithelial (Clara) cells, myocardial infarction (MI) where they become myofibroblasts (MFs), and liver regeneration where they give rise to Kupfer cells and other hepatic cells yet to be identified. Moreover, we have shown that: 1) phenotypic switching of cultured SMC is mediated by activation of the embryonic stem cell (ESC) and induced pluripotential stem (iPS) cell pluripotency factors Oct4 and Klf4; and 2) SMC-P specific conditional Klf4 knockout mice show profoundly impaired cardiac repair following MI. Taken together, results support the hypothesis that perivascular cells represent a source of mesenchymal stem cell (MSC)-like cells that play a key role in tissue regeneration and repair, and that phenotypic transitions of these cells are mediated via stem cell pluripotency gene networks. This hypothesis will be tested by addressing three specific aims. Aim 1 will test the hypothesis that SMC-Ps activate ESC pluripotency networks and give rise to multiple other cell types in the setting of injury-repair. Aim 2 will tes the hypothesis that H3K4diMe of SMC marker and regulatory genes not only provides an epigenetic signature of SMC lineage, but also provides a mechanism for SMC lineage memory during reversible phenotypic switching following carotid wire injury and that this biases the cells into re-differentiating into a SMC once the vascular repair is complete. Aim 3 will test the hypothesis that transitions in SMC-P phenotype and/or trans-differentiation to alternative cell types in the setting of injury-repair are dependent on activation of the ESC pluripotency genes Klf4 and Oct4, and are mediated at least in part through epigenetic mechanisms. Studies will define mechanisms that regulate transitions of SMC-P to MSC-like cells in vivo, and may contribute to development of novel therapeutic approaches for enhancing stem cell like properties of SMC-P in vivo to augment tissue repair following injury, and/or to treat a wide plethora of major human diseases.